Wow, Thanks Robin, AJ, & Beezlebum for your thoughtful input! I hadn’t recognized that the two-stroke schematic was calling for a 6.3v center-tapped heater circuit. I’ve read valvewizard’s pieces on so many topics- I hadn’t seen the one you linked to, so thanks again for that.
I’ve seen someone’s pictures of the process. Maybe I can find that again.
So much to learn, so little room for error.